Assays for the detection of target biomolecules within a sample, especially of multiple target biomolecules within a sample, are often performed by applying a volume of the sample to a test slide, membrane, or other substrate having immobilized reactants which may interact with the target or targets to form detectable complexes. These immobilized reactants are usually disposed at fixed locations, with samples brought to these locations. U.S. Pat. No. 5,139,743, for example, discloses a biochemical analysis apparatus wherein an applicator takes up a liquid sample and applies the sample to a fixed position test film for chemical analysis of the sample.
Sometimes complexes of target biomolecules and reactants are visually detectable directly after an appropriate incubation period for the sample and reactants, or after numerous development steps wherein development chemicals, such as fluorescent dye-conjugated molecules, are allowed to interact with the complexes. For example, the detection mechanism in U.S. Pat. No. 5,296,194 involves optically detecting a color change in a blood drop applied to a test slide.
U.S. Pat. No. 4,877,745 discloses methods for preparing immobilized reagents and applying samples to immobilized reagents. In particular, this patent discloses dispensing precisely controlled volumes of droplets onto a medium at precisely controlled locations, to form arrays of immobilized reagents by a jet head. An x-y plotter may be modified to carry a jet head so that reagent may be dispensed over an area.
Robotic laboratory workstations, such as the Biomek 1000 and 2000 of Beckman Instruments, Inc. have been developed for automatically carrying out assays involving multiple reactants and multiple samples. Typically such workstations are designed to deliver robotically precise volumes of reactants to a number of different samples located at known areas within the workstation. Alternatively, workstations can robotically move samples to reagents.
U.S. Pat. No. 5,171,537 to Wainwright et al. teaches activated immunodiagnostic pipette tips. The pipette tip houses a spherical element which is coated with a single ligand having affinity for a target molecule of a sample. With this device, the test element may be brought to contact the sample, as by aspirating the sample into the pipette tip. These pipette tips are limited in their sample throughput because they house only a single ligand reagent and thus preclude the detection of multiple analytes within a sample.
A class of devices known as optical biosensors, characterized by immobilized assay species within a supporter and a light collection device coupled to an optical waveguide, is also known. Optical biosensors may be used for detecting and quantifying the presence of specific species in test fluid samples, such as in clinical diagnostic reactions. For example, U.S. Pat. No. 4,857,273 discloses an optical biosensor for immunoassays and certain other reactions. Other examples, involving use of an optical fiber, are U.S. Pat. No. 5,143,066 and U.S. Pat. No. 5,401,469.
It is an object of the present invention to provide apparatus and methods for rapidly and automatically determining the presence of multiple target biomolecules in a single sample. It is another object of the present invention to provide analytical methods which require minimal sample volume and a minimal number of liquid transfers. It is a further object of the present invention to provide a device and system for rapid assessment of samples for target biomolecules which is readily adaptable to a variety of chemical and other detection schemes.